Living coral: red and yellow sea fan (Acabria sp.) off the coast of Borneo, Malaysia.

Credits: © International Coral Reef Information Network / Jeff Dawson

Coral reefs are threatened by pollution, destructive fishing practices, coastal development, careless tourism and climate change. Ocean warming is extremely dangerous to coral organisms, which are very sensitive to changes in temperature. Increased water temperatures, which may be linked to global warming, can cause mass coral bleaching. Dissolved carbon dioxide also damages corals.

Coral reefs face numerous hazards and threats. As human populations and coastal pressures increase, reef resources are more heavily exploited, and many coral habitats continue to decline. In many areas, coral reef habitats are overfished and/or overexploited for recreational and commercial purposes. Coral heads and brightly coloured reef fishes are collected for the growing aquarium and jewellery trade. Careless or untrained divers often can trample fragile corals. In addition, their fishing techniques can be destructive not only to fish but to the coral habitat. Blast fishing, for example, in which dynamite or other heavy explosives are detonated to stun fish for easy capture. Other damaging fishing techniques include deep-water trawling, which involves dragging a fishing net along the sea bottom, and muro-ami netting, in which reefs are pounded with weighted bags to startle fish out of crevices.

Coral reefs are also directly impacted by marine-based pollution. Leaking fuels, anti-fouling paints and coatings, and other chemicals can leach into the water, adversely affecting corals and other species. Reefs are dependent on specific environmental conditions. Most require a specific water temperature range (23 to 29°C) for optimal growth. Some can tolerate higher temperatures, but only for limited periods of time. In addition, specific levels of salinity (32 to 42 parts per thousand), water clarity and light levels generally must be consistent throughout the year for corals to grow optimally. Many scientists, however, believe that impacts associated with global climate change, such as increased concentrations of carbon dioxide and other greenhouse gases, are disrupting the delicate balance of the ocean’s chemistry. Warming trends can elevate seawater temperatures and levels as well, rendering conditions unfit for coral survival. Current estimates note that 10 per cent of all coral reefs are degraded beyond recovery. Thirty per cent are in critical condition and may die within 10 to 20 years. Experts predict that if current pressures are allowed to continue unabated, 60 per cent of the world's coral reefs may die completely by 2050.

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